The invention relates to a system for triggering passive occupant safety measures in a motor vehicle, having a control unit, a plurality of acceleration sensors for detecting the acceleration caused by an impact of the motor vehicle at different locations of the motor vehicle as well as feed lines assigned to the acceleration sensors, by which feed lines the output signals of the acceleration sensors are transmitted to the control unit which analyzes value-continuous output signals at least of some of the acceleration sensors, determines the type and/or severity of the impact from the output signals and, as a function thereof, triggers appropriate safety measures.
Passive safety measures for the protection of the occupants of a motor vehicle are triggered on the basis of signals which are typically obtained from sensors mounted in a distributed manner in the vehicle. With a view to the timely triggering of such safety measures adequate for any situation, the appropriate spatial mounting of the sensors and their reliability are extremely important.
For being able to judge, in addition to the occurrence of an impact, also its type and severity, it is advantageous to detect the time behavior of the acceleration acting upon different parts of the vehicle. For this purpose, acceleration sensors are frequently used in passive occupant safety devices. These are typically suitable for supplying a value-continuous signal as the output signal which is proportional to the active acceleration. Likewise, there are sensors in the case of which an acceleration signal is already integrated in the sensor, and a speed signal or position signal is thereby emitted. In the following, such sensors will also be called acceleration sensors.
In addition to acceleration sensors in the above-mentioned sense, sensors are frequently used which change their output signal only when the acceleration, speed or deformation acting upon them exceeds a certain threshold. In the following, such sensors will be called binary sensors. Sensors which supply a value-continuous signal will also be called binary sensors in the following. However, this value-continuous signal will only be analyzed in a threshold-based manner for obtaining a binary signal by a control unit to which the signal is transmitted.
For the rapid detection of an impact, particularly of a frontal impact, numerous systems are known in which so-called front sensors are mounted close to the outer vehicle circumferences. From U.S. Patent Document U.S. Pat. No. 3,861,488, a sensor for the detection of an impact speed is known, which is mounted directly on the side of a bumper facing the vehicle interior. However, no devices for differentiating between a safety-relevant impact of the vehicle and non-safety-relevant disturbing influences are provided in the described safety system. The high probability of a faulty triggering connected therewith should be considered to be a serious disadvantage of a passive safety device. Furthermore, the used sensor and its feed line in the described embodiment, which is characterized by a particularly exposed mounting site, are insufficiently protected from environmental influences (weather, splashing water, etc.), which may have a disadvantageous effect on the durability of these components and may lead to a malfunction.
The most frequent mounting site of front sensors according to the state of the art is a vehicle body part close to the outer vehicle circumferences defined by the bumpers of the vehicle. For example, a passive safety device is known from U.S. Patent Document U.S. Pat. No. 4,995,639, in which a front sensor is mounted on a forward cross member of the vehicle. With respect to the measurability and analyzability of the sensor signals, this type of mounting has the disadvantage that, because of the stiffness of the vehicle body, which is high in comparison to the bumpers, very high acceleration peaks act upon the acceleration sensor within a relatively short period of time in the case of an impact. The high stiffness of the vehicle body may also increase the occurrence of mechanical resonance vibrations which are superimposed on the acceleration signal to be measured and make its analysis difficult. In addition, in the case of a mounting of an acceleration sensor displaced from the outer vehicle circumferences to the vehicle interior—FIG. 1 of U.S. Patent Document U.S. Pat. No. 4,995,639 does not show all relevant vehicle parts—, only an indirect mechanical coupling exists between the point of impact and the mounting site of the acceleration sensor. The mechanical transmission of the impact energy by way of this indirect mechanical coupling causes a falsification of the acceleration measured by the acceleration sensor in comparison with the acceleration acting at the outer vehicle circumferences. As a result, an impact can be detected only very late and can be judged only imprecisely with respect to its type and severity. This applies particularly to an impact of low or medium intensity. As demonstrated by investigations, a more severe impact can be better detected by sensors mounted at other measuring sites.
In the following, an impact of low or medium severity is defined as an impact at a relative impact velocity of up to 40 km/h against a soft object or at a relative impact velocity of up to 30 km/h against a hard object.
A passive safety system having front sensors mounted directly on the forward bumpers is known from German Patent Document DE 101 42 925 C1. However, in this case, the front sensors are constructed as binary sensors which are used only for the early detection of an impact. The assessment of the type and severity of an impact takes place on the basis of acceleration sensors arranged farther in the vehicle interior. The disadvantages with respect to the detection and assessment of an impact of low or medium severity, which accompany the indirect mechanical coupling between the impact site and the sensor mounting site resulting from the mounting in the vehicle interior, were explained above
The present invention provides a system for triggering passive safety measures which has a low risk of malfunctioning and permits an early impact detection and a precise assessment of the type and/or severity of an impact. In particular, an early detection and a precise assessment should take place with respect to an impact of low or medium severity.
This is achieved by using a passive safety system in which the acceleration sensors provided for receiving signals are mounted on vehicle parts of low structural stiffness on the outer vehicle circumferences. These vehicle parts are constructed with respect to shape, arrangement and material such that, after an impact of low or medium severity of the motor vehicle, the acceleration sensors will not come in contact with vehicle parts of high structural stiffness within a minimum reaction time period.
In the event of an impact of the vehicle upon an object, the highest acceleration values act upon those vehicle parts which are situated closest to the impact site on the outer vehicle circumferences. Likewise, for such vehicle parts, the maximum amount over time of the acceleration following an impact is reached at a very early point in time. This applies particularly when the above-mentioned vehicle parts have a low structural stiffness, and thus react to the impact with a high deformation and therefore high acceleration values. If an acceleration sensor is mounted on such a vehicle part, an impact close to the mounting site of the acceleration sensor causes a very early and considerable change of the output signal of the acceleration sensor.
The direct mechanical coupling between an impacting object and a vehicle part on the outer vehicle circumferences close to the impact site results in a direct mechanical coupling between the impacting object and an acceleration sensor mounted on the vehicle part. The acceleration acting upon the impact site therefore acts in a genuine manner or in a less falsified manner upon the acceleration sensor than in the case of the mounting of the acceleration sensor at a different site of the vehicle. The time behaviors of the acceleration which can be received by an acceleration sensor mounted according to the invention, with respect to the signal quality and value range, are therefore typically suitable for a value-continuous analysis.
The early providing of mechanically genuine, value-continuously analyzable acceleration time behaviors taking place by a system according to the invention, in the case of a corresponding signal transmission and analysis, permits a precise and reliable assessment of the type and severity of an impact, and thus promotes the triggering of adequate passive safety measures. The safety of the vehicle occupants is thereby greatly improved.
The mounting of an acceleration sensor on a vehicle part of a low structural stiffness has the advantage that, in contrast to the mounting on a vehicle body part, the effect of vibrations not relevant to safety upon the acceleration sensor is reduced.
Another significant advantage of a system according to the invention is the fact that the acceleration acting upon the acceleration sensor during an impact lasts for a longer period of time in contrast to a mounting on a vehicle body part. As a result of the longer reaction time, a time behavior signal can be obtained which can be analyzed better and can be used, for example, in a control unit for a comparison with patterns filed there in a database. In this case, a minimum length of the reaction time period of, for example, approximately 40 ms, which in the following will be called a minimum reaction time, is desirable. The precise minimum reaction time depends on the method used for assessing the impact.
However, a minimum reaction time can only be guaranteed if, even in the event of a deformation of the vehicle resulting from an impact, the acceleration sensor is not destroyed within the minimum reaction time period or fails for other reasons. A minimum reaction time period is the time period of the length of the minimum reaction time which starts at the moment of the impact between the vehicle and the object.
In order to prevent the destruction of the acceleration sensors within the minimum reaction time period, in a system according to the invention, the acceleration sensors are mounted such that, and all vehicle parts are constructed with shapes arrangements and materials such that contained acceleration sensors, after an impact and within the minimum reaction time period, do not come in contact with vehicle parts of a high structural stiffness.
According to a further exemplary embodiment of the invention, a deformation space is provided for this purpose on the side of the acceleration sensor facing the vehicle interior, which deformation space is either hollow or is filled exclusively with vehicle parts of a low structural stiffness. Toward the vehicle exterior, the deformation space is preferably bounded by a plane extending through the acceleration sensor, whose normal line points from the acceleration sensor to the vehicle interior. The shape of the deformation space toward the vehicle interior is defined by the shape and arrangement of the adjacent vehicle parts. Deformations of these vehicle parts cannot change the deformation space.
Instead of a plane through the acceleration sensor, a hyperplane, for example, conically starting out from the acceleration sensor can also be defined as a more restrictive boundary of the deformation space toward the vehicle exterior. In this manner, possible deformation-caused movement directions of the acceleration sensor can be taken into account. According to the invention, the plane or hyperplane is selected such that the acceleration sensor is always, particularly in the case of an impact, situated completely on the vehicle interior side of the plane or hyperplane.
If such a deformation space already exists on a vehicle part on the side, which faces the vehicle interior, of a site in principle suitable for the mounting of an acceleration sensor according to the invention, an acceleration sensor may be mounted on this site.
Depending on the point of view, the acceleration sensor itself may be situated within the deformation space or on the edge of the deformation space assigned to it, which edge points to the vehicle exterior. In the event of an impact, the acceleration sensor is displaced farther into the interior of the deformation space as a result of the deformation of the motor vehicle part to which it is fastened. Because of the fact that no vehicle parts of a high structural stiffness are situated in the deformation space, it is ensured that the acceleration sensor is not destroyed as a result of the contact with a vehicle part of a high structural stiffness, as long as it is situated completely in the interior of the deformation space.
The dimensions of the deformation space to be provided, particularly its depth toward the vehicle interior, are defined by the range of the impact velocities to be detected by the acceleration sensor, and by the minimum reaction time and the structural stiffness of the vehicle part on which the acceleration sensors is mounted. If information is available in this respect, the mass, the shape, the stiffness, the speed and additional physical quantities of impacting objects can also be taken into account during the assessment. In principle, the dimensioning of the deformation space can take place on the basis of limit value estimates and/or computations and/or simulations, such as FEM.
Because of advanced development and manufacturing methods, the deformation space can already be taken into account in the early development process of a vehicle and, as a rule, can be implemented in the manufacturing process with the lowest possible increase of manufacturing expenditures. Whether a certain dimensioning guarantees a desired minimum reaction time in the event of an impact of a predefined type or severity or permits a highly probable expectation, can be verified during the development process, for example, by simulations on data models, particularly virtual prototypes.
In addition to the avoidance of the mechanical destruction of the acceleration sensors themselves, the availability of suitable output signals of the acceleration sensors for the analysis in the control unit also depends on whether the mechanical destruction of the feed lines of the acceleration sensors can be prevented in the event of an impact.
For reasons of simplicity, it is assumed in the following that each acceleration sensor has a single feed line which connects it directly with the control unit. However, the carried-out considerations can easily also be applied to the indirect linking of the acceleration sensors to the control unit by way of other components of a data bus system and/or a mutual networking of the acceleration sensors. Such embodiments are therefore also within the scope of the invention. Likewise, by using the control unit, which may consist of one or several components, additional sensors can be analyzed for the same or a different purpose. Depending on the type of acceleration sensor, as required, the feed line may supply the acceleration sensor with a supply, offset or reference quantity needed for its operation.
According to a second exemplary embodiment of the invention, the feed line of the at least one acceleration sensor has an elastic, preferably flexible construction and extends inside a feed line duct defined by the shape, arrangement and possibly deformation of the adjacent vehicle parts. The mechanical destruction of the feed line can then be excluded with a high probability if, in the event of an impact, this feed line duct is not interrupted at any point by the deformation of vehicle parts and if, as a result of the deformation, the length of the feed line duct does not change such that the length of the feed line is no longer sufficient for extending through the entire feed line duct. According to the above-mentioned second exemplary embodiment of the invention, the shape, arrangement and material of all vehicle parts are therefore designed such that, within a minimum reaction time period after an impact of the motor vehicle of low or medium severity, the smallest diameter of the feed line duct remains larger than the diameter of the feed line.
A first requirement is that the cross-section of the feed line is substantially constant and circular along the length of the feed line. In the case of a feed line having a cross-section that is not constant and/or not circular, correspondingly higher expenditures have to be considered for the remaining feed line duct. Such a consideration and the construction of the vehicle parts forming the feed line duct derived therefrom are also within the scope of the invention.
In addition, according to the above-mentioned second exemplary embodiment of the invention, the required length of the feed line, while taking into account an elasticity of extension, as well as the arrangement and the fastening of the feed line on the vehicle parts are constructed such that the feed line can adapt itself to a plurality of conceivable movements of the acceleration sensor and changes of the feed line duct caused by the deformation of vehicle parts, particularly all movements resulting from an impact of the motor vehicle of low or medium severity within the minimum reaction time period, and changes of the feed line duct, without tearing off or being damaged.
Similar to the above-mentioned deformation space, the dimensions and the precise shape of the feed line duct to be provided are defined by the range of the impact velocities to be detected by the acceleration sensor, using the minimum reaction time, using the structural stiffnesses of the vehicle parts forming the feed line duct as well as using the structure of the vehicle parts situated between the feed line duct and a potential impact site on the vehicle. If information is available for this purpose, as in the case of the dimensioning of the deformation space, the mass, the shape, the stiffness, the velocity and additional physical quantities of impacting objects can also be taken into account during the assessment. In principle, the dimensioning of the feed line duct can take place on the basis of limit value estimates and/or computations and/or simulations such as FEM.
Because of the exposed mounting on the outer vehicle circumferences implied therein, the above-mentioned advantages of a system according to the invention are bought by the necessity of a robust construction of the acceleration sensors and their feed lines with respect to environmental influences, particularly moisture.
In contrast to most acceleration sensors used according to the state of the art, the housing of an acceleration sensor used in a system according to the invention includes a moisture-resistant construction. Likewise, the connection site between the housing and the feed line of the acceleration sensor has a moisture-resistant construction.
The use of a hydrolytically stabilized material for the housing of an acceleration sensor used in a system according to the invention is particularly advantageous in the embodiments according to the invention.
A particularly high resistance to moisture can be achieved if, as an alternative or in addition, the housing of the acceleration sensors is laser welded, particularly if it has a laser-welded lid.
Devices for a pressure compensation are provided on the housing of an acceleration sensor used in another particularly preferred exemplary embodiment of a system according to the invention. By using a pressure compensation, it can be prevented that, as a result of a vacuum in the housing interior, moisture is sucked into the housing interior.
In addition to the resistance to moisture, when constructing the acceleration sensors and feed lines, because of their exposed mounting in the vehicle, a high robustness with respect to mechanical damage such as bursting of the sensor housing, tearing off or breaking of the feed line has to be ensured. However, by advanced techniques in the manufacturing of acceleration sensors and feed lines, the above-mentioned demands can be met.
The moisture-resistant housings for the exemplary acceleration sensors used according to the invention have a high elasticity. Elastic materials are less susceptible to destruction than the materials used in the systems according to the state of the art in the case of a deformation-caused contact with vehicle parts, which ideally is to be avoided, and/or in the case of a deformation of the vehicle part on which the acceleration sensor is mounted. According to the state of the art, acceleration sensors are, for example, mostly accommodated in metal housings with a glued-on lid. When elastic housings of the acceleration sensors are used, vibrations of the vehicle part on which the acceleration sensor is mounted cause lower interference signals than when stiffer housings, such as metal housings, are used.
In addition to the use of flexible and ideally also elastically extensible materials for the feed lines, the mechanical securing of the feed lines predominantly already takes place in the early development process of a vehicle.
In the previous consideration, it was assumed that the acceleration acting upon an acceleration sensor mounted on the outer vehicle circumferences largely corresponds to the acceleration of the surrounding vehicle parts, and the output signals of the acceleration sensor therefore supply a good representation of the acceleration acting upon the corresponding vehicle parts.
In the case of the use of acceleration sensors with a preferred effective direction, an assessment of the type and severity of an impact based on this prerequisite can, however, reliably take place only if the acceleration sensor is mounted on the outer vehicle circumferences such that, in the event of an impact, they are not rotated out of their preferred effective direction. For an optimal receiving of signals by the acceleration sensors, care should therefore be taken that the acceleration caused by an impact and acting upon the acceleration sensor has a high translatory component and a rotatory component which is as low as possible.
In order to ensure a predominantly translatory acceleration in the event of an impact, it is particularly advantageous for the cross-section of the acceleration sensor to overlap in the direction of the vehicle interior essentially with the cross-section of a supporting element on the vehicle part carrying the acceleration sensor. If, for constructive reasons, an overlapping is not possible, a distance that is as small as possible (for example, less than 10 cm) is desirable.
According to a preferred exemplary embodiment of the invention, an acceleration sensor used in a system according to the invention is therefore positioned such that the cross-section of the acceleration sensor in the direction of the vehicle interior, is at a narrow distance from the cross-section of a supporting element, such as an impact absorber.
If permitted by the constructive marginal conditions, an acceleration sensor according to a particularly preferred embodiment of the invention is positioned such that its cross-section in the direction of the vehicle interior substantially overlaps with the cross-section of a supporting element.
If, on the other hand, acceleration sensors are used which are capable of detecting by measuring techniques accelerations in several directions and/or a rotation, particularly about the own vertical axis, a rotation of an acceleration sensor must not necessarily be avoided by constructive measures, but can be taken into account mathematically when analyzing its output signals.
The output signals of the acceleration sensors are transmitted to a control unit by way of feed lines. The control unit is suitable of determining the type and severity of an impact, for example, by comparing of the recorded value-continuous acceleration signals with stored reference data. In particular, the control unit of an advantageous device according to the invention is suitable for differentiating using the output signals of the acceleration sensors between an impact of the vehicle and disturbing influences which are not relevant to safety.
As a function of the type and severity of an impact, the control unit triggers suitable safety measures. The triggering of suitable safety measures may also comprise the triggering of preparatory measures which have the effect that one or more safety measures triggered later take place in an improved, for example, faster manner.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.